Food Chemistry

19.1 Sugars, Sugar Alcohols and Sugar Products 871

alkaline degradation of sugar occurs to a small

extent, and darkening of the syrup occurs due

toMaillardreaction and caramelization, de-

pending on the process management (tempera-

ture, residence time in the evaporation stages).

• Crystallization. Multistage crystallization can
  be used to isolate 85−90% of the sucrose
  contained in the thick syrup. The remaining
  sucrose and practically all the non-sugar
  substances are found in the last mother
  liquor called molasses. The crystallization
  process is predominantly a discontinuous
  operation. However, efforts are being made to
  introduce a continuous process (evaporative
  crystallization and centrifugation).
  The thick syrup is evaporated in a boiling
  apparatus at 0.2–0.3 bar and 65–80◦C until
  slight supersaturation is achieved (evaporative
  crystallization). Crystallization is then initi-
  ated by seeding, e. g., by adding a dispersion
  of sucrose crystals (0.5–30 μm) in iso-
  propanol. The mixture is further boiled until
  the crystals acquire the required size. In this
  process, the formation of both new crystals
  and crystal conglomerates is to be carefully
  prevented by intensive circulation (steam gen-
  eration, stirring). The crystal paste (magma)
  with a crystal content of 50–60% is discharged
  into mashers for homogenization with con-
  stant stirring at a constant temperature.

Fig. 19.7.Crystallization scheme for the production of A) raw sugar, B) white sugar, and C) refined sugar. The
yields of sucrose (%), based on the amount of sucrose added with the thick syrup, are given in brackets behind the
final products (underlined)

A further crystallization occurs in part on

very slow cooling to 35− 40 ◦C (cooling

crystallization). In this process, the viscosity

of the mash must be maintained constant by

the addition of water or mother syrup. Today,

cooling crystallization is generally used only

for after-product magma, but it will be of

importance for raw sugar and white sugar.

Subsequently, the crystalline sugar from

the mashers or massecuite is centrifuged in

centrifugal baskets, eliminating the mother

liquor called green syrup, which is returned to

the process. The sugar (with the exception of

raw sugar) is then freed from adhering syrup

by washing with hot water and steam in the

centrifuge. The resulting sugar solution (wash

syrup) is fed back to the crystallization pro-

cess. The presence of higher concentrations

of raffinose in the magma (>1%, based on

dry matter) reduces the rate of crystallization

of sucrose and produces needle-shaped crys-

tals. For this reason, raffinose is cleaved by

α-galactosidase.

In this manner, thick syrup can be processed

into raw sugar or consumer sugar (white

sugar and refined sugar), depending on the

process operation. The different crystalliza-

tion schemes are simplified in Fig. 19.7.

Raw sugar contains 1− 1 .2% of organic and

0. 8 −1% of inorganic nonsugar substances